Generally, CATV transmission cables are connected to subscribers via multi-tap distribution apparatuses. CATV stations transmit through the cables not only television signals and control signals but also currents for operating main line amplifiers.
While some distribution apparatuses are not designed for passing currents, there are those designed for this purpose. The later type of distribution apparatuses are provided with a current transmission circuit either installed in the high-frequency passing route or installed as a separate circuit. The aforementioned high-frequency passing route originating in a cable connecting portion and leading to taps via a branch circuit and a distribution circuit.
In the latter type of distribution apparatus, the large currents that are conducted through the main line pass at least through the cable connecting portions, although only low ampere currents reach the taps. Therefore, it is necessary to secure sufficient capacity in the transmission line in order to minimize both the transmission loss and adverse effect on the characteristics of the electromagnetic waves.
The most effective measure would be to use a thick coaxial cylinder for the transmission line. This, however, is not a very practical measure because it takes up too much space in the distribution apparatus, leaving less space for installing other circuits. This measure also increases the number of parts, thereby increasing assembly time and cost.